Considerable pressure variations are often encountered in hydraulic systems that include hot-water and cold-water supply lines. These pressure variations are due to large, unforeseen drops in hot or cold water supply pressure. The pressure drop occurs if another faucet, a dishwasher, a washing machine or the like is turned on, or a toilet is flushed. This pressure drop results in rapid change of water temperature. In order to prevent this disturbing phenomenon a pressure balancing device is disposed in the system which compensates for pressure variations between cold and hot water supply pipelines by restricting the flow from the pipeline with the higher pressure.
Generally pressure balancing devices are of two main types: pressure balancing devices with deformable membrane and pressure balancing devices with sliding box. Both of these types of pressure balancing valves exhibit certain characteristic advantages and disadvantages.
The pressure balancing valves with a membrane comprise a mobile unit which is supported by a tight deformable membrane, and which moves when there are pressure differences between the supply lines in order to partially choke or restrict the pipeline with the greater pressure. The presence of the membrane ensures a separation between the supply lines. But the membrane itself confers features of instability upon the device. The membrane easily generates vibrations and, under certain conditions, these vibrations can attain a seriously disturbing intensity. Furthermore, in view of the structure of these devices, although the membrane may have a relatively large diameter, the useful active cross-section upon which the pressures act for the operation of the device turns out to be rather limited, so that it is necessary to make these devices relatively large in order to obtain proper operation.
Pressure balancing devices with a sliding box comprise a piston box mounted in the bore of a body which contains supply lines. They are less subject to instability and to major vibrations but they do not provide separation between the supply lines, thereby requiring nonreturn valves in the supply lines. Furthermore, the piston box has a small diameter when compared to the general dimensions of the device, and the pressure forces applied upon the box are small. Consequently, the box cannot be provided with a retaining packing or seal because that would give rise to excessive wear and tear, which impairs the operation of the device. Therefore, the box and the pertinent bore must be precision machined, which is expensive and results in easy clogging. Finally, the requirement for precision machining necessitates a metal structure from the main parts, and this leads to formation of calcium deposits that obstruct the operation and can lead to the blockage of the device.
In view of the above, the main purpose of this invention is to provide a pressure balancing device that will not be subject to phenomena of instability or to vibrations, a device that will not require particularly expensive machining, that will ensure separation between the supply lines, and in which the useful cross section subject to pressures will be as great as possible in relation to the external dimensions of the device so as to permit the production of embodiments with reduced size to enable their installation in small bodies or cartridges.